This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-085991, filed Mar. 29, 1999; No. 11-250513, filed Sep. 3, 1999; and No. 11-318816, filed Nov. 9, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a control system including a main controller and multiple unit controllers each of which has sensors and actuators connected to it.
Heretofore, medium carrier apparatuses for moving media, say, paper, are equipped with a number of sensors (e.g., optical sensors) for detecting the position and state of the media and a number of actuators for separating and moving the medium. Thus, how to transmit actuator- and sensor-related signals to/from a CPU becomes an important problem.
The most straightforward method is to connect simply signal lines associated with all sensors and actuators to the circuit board of a main controller. Another example is line concentration as disclosed in Japanese Patent Publications No. 62-31393 and No. 4-53359.
More specifically, according to the technique disclosed in Japanese Patent Publication No. 62-31393, a signal produced by each sensor is converted into a binary signal representing light and shade by comparing its level with a threshold, called a slice level and the resulting binary signal is then transmitted to a CPU. In the technique disclosed in Japanese Patent Publication No. 4-53359, each sensor signal is converted into a multivalued digital signal according to its level and bits of the resulting digital signal are then transmitted serially.
Continuously turning on the actuators may result in coil burning and machine destruction. It is therefore required not to continue turning on the actuators over a fixed time. In view of this point, control is performed in such a way as to measure time and turn off the actuators after a lapse of a fixed time with a CPU program.
In general, a mechanism section at the start of operation needs more power than is needed after the operation has been started. Control is then performed in such a way as to supply a large current only at the start of operation to create great power and reduce current during the operation and in the hold state after the operation has been completed to thereby reduce power dissipation and heat generated by the actuators.
However, with the aforementioned method to connect all sensor signal lines to the main controller circuit board, long signal lines are required to connect the sensors to the board, resulting in an increase in cost. In addition, depending on the number of signal lines, packaging may become difficult. Moreover, there exists a problem that the signal lines that transmit analog signals are susceptible to noise.
With the technique to transmit binary signals as in Japanese Patent Publication No. 62-31393, the sensor signal level drops gradually due to the life of parts, the effect of ambient temperature, accumulation of dust on parts, and variations in parts mounting accuracy, resulting in failure of proper binarization. In order to compensate for the drop in signal level with time, it is conventionally required for technical personnel to, at regular intervals, measure the level of each sensor signal and adjust the slice level according to measurements. This is a heavy burden to the technical personnel.
With the technique to convert each sensor signal into a digital value (multivalued data) for serial transmission as in Japanese Patent Publication No. 4-53359, the amount of data transmitted from each sensor increases, resulting in the increased interval of transmission from each sensor and consequently in the reduced monitoring accuracy of each sensor. In some cases, the number of sensors that are accommodated may be limited.
The prior art techniques, intended to concentrate signal lines for sensors only, require separate signal lines to control actuators, resulting in an increase in the number of serial lines. It is uneconomical to use many serial lines.
Hereinafter, this problem will be discussed in detail.
First, when all the signal lines are connected to the main controller, the average length of signal lines is much increased, which is uneconomical and may make packaging difficult due to an excess of wiring. In addition, the sensor signal lines, which are long in analog signal transmit portion, are susceptible to noise.
Second, the line concentration only for sensor signal lines suffers from the following problems:
If the sensor output level is transmitted as it is, the line traffic will increase. When the sensor level is transmitted in binary form (on/off) or when the sensor output is two-valued, the setting of a light/shade threshold cannot be automated because the CPU cannot know the sensor output level. Further, the degree of allowance for lowerings of sensor outputs in light condition is small. In addition, actuator control lines are required in addition to sensor circuit control lines.
In summary, with the technique disclosed in Japanese Patent Publication No. 62-31393, since only the on/off state is detected and transmitted, it is impossible for the CPU to know the analog level at on time. Thus, the on/off threshold cannot be altered or, if alterable, it is required to measure the sensor level with a separate measurement instrument and set manually a threshold derived from the measurements.
The technique disclosed in Japanese Patent Publication No. 4-53359, adapted to transmit a digital value corresponding to an analog level as it is, has a problem that the amount of data over data lines increases and it is therefore required to reduce the number of sensors that can be accommodated at the same data transmission rate or to reduce the transmission interval, i.e., the time accuracy of monitoring. In addition, since only the transmission lines for sensor information are concentrated and the controller usually controls motors and solenoids, lines for transmitting actuator operating commands from the CPU and lines for sending the results of control and state information to the CPU are required to be provided separately. This is uneconomical.
With the method to prevent coil burning and machine damage through the use of a CPU program, not only the amount of processing by the CPU increases but, in the event that the CPU causes runaway due to defects in the program or the like, the preventive facility does not work properly, so that coil burning and machine damage result.
It is therefore an object of the present invention to provide a control system which permits information captured by each sensor to be sent exactly to a main controller and a fall in the level of sensor signals with time to be automatically compensated for with no need to make sensor signal lines long and without reducing the sensor monitoring accuracy and limiting the number of sensors used.
It is another object of the present invention to provide a control system which has a main controller having a CPU and each of unit controllers for directly controlling unit mechanisms connected together through serial lines and shares the serial lines for a sensor monitoring function and an actuator control function, thereby allowing the number of the serial lines to be reduced.
It is still another object of the present invention to provide a control system which automatically turns off output ports a fixed time after they are turned on to thereby reduce loading of a CPU and improve safety in the event of a CPU malfunction.
To achieve the objects, according to a first aspect of the present invention there is provided a control system having a main controller and one or more unit controllers each of which has one or more sensors connected, comprising: select means, provided in each of the unit controllers, for selecting sensor signals produced by the sensors in sequence; comparison control means, provided in each of the unit controllers, for making a comparison between the level of a sensor signal produced by each of the sensors and a prestored threshold level and holding the result of each comparison; control means, provided in each of the unit controllers, for converting the contents of the comparison control means into a serial signal and transmitting the serial signal to the main controller; recognition means, provided in the main controller, for recognizing the results of comparisons sent in serial form from each of the unit controllers; and slice level change means, controlled by the main controller, for changing the level stored in the comparison control means.
According to a second aspect of the present invention, there is provided a control system having a main controller and a plurality of unit controllers each of which has a plurality of sensors connected, comprising: select means, provided in each of the unit controllers, for selecting sensor signals produced by the sensors in sequence; A/D conversion means, provided in each of the unit controllers, for converting the level of each of the sensor signals selected by the select means into digital data; comparison control means, provided in each of the unit controllers, for making a comparison between output data of the A/D conversion means and prestored each of the slice levels for the sensors and holding the result of each comparison; designate means, provided in the main controller, for designating each of the unit controllers; control means, provided in each of the unit controllers, for, when the corresponding unit controller is designated by the designate means, converting the contents of the comparison control means into a serial signal and transmitting the serial signal to the main controller; recognition means, provided in the main controller, for converting the results of comparisons sent in serial form from each of the unit controllers into parallel form and recognizing them;
and slice level change means, controlled by the main controller for changing the level stored in the comparison control means.
According to a third aspect of the present invention, there is provided a control system having a main controller and a plurality of unit controllers each having one or more sensors connected and one or more output ports, comprising: a sensor circuit, provided in each of the unit controllers, for transmitting sensor information serially over a first serial line to the main controller; port information transmit means, provided in the main controller, for transmitting ON/OFF information for each of the output ports in each of the unit controllers over a second serial line to the unit controller; an output port circuit provided in each of the unit controllers and responsive to the ON/OFF information for the output ports transmitted from the port information transmit means for performing ON/OFF control of each of the output ports; and command transmit mean s provided in the main controller for transmitting a command signal for controlling the operating state of the sensor circuit and a command signal for controlling the operating state of the output port circuit over a third serial line to each of the unit controllers.
According to a fourth aspect of the present invention, there is provided a control system having a main controller and one or more unit controllers having one or more output ports, each of the unit controller s including: clock generating means for generating a clock signal; counter means for counting the clock signal and producing a forced OFF signal at the time when a preset clock count is reached; ON/OFF information hold means for holding ON/OFF information for the output ports; edge detect means for detecting a change in the ON/OFF information in the ON/OFF information hold means and providing a count enable signal to the counter means at the time when the change is detected; and control means for instructing the counter means as to either whether to output the forced OFF signal or not or whether to count the clock signal or not according to an operation mode set by the main controller.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.